The Role of Metallurgical Features in the Microbially Influenced Corrosion of Carbon Steel: A Critical Review.

Microbially influenced corrosion (MIC) is a potentially critical degradation mechanism for a wide range of materials exposed to environments that contain relevant microorganisms. The likelihood and rate of MIC are affected by microbiological, chemical, and metallurgical factors; hence, the understanding of the mechanisms involved, verification of the presence of MIC, and the development of mitigation methods require a multidisciplinary approach. Much of the recent focus in MIC research has been on the microbiological and chemical aspects, with less attention given to metallurgical attributes. Here, we address this knowledge gap by providing a critical synthesis of the literature on the metallurgical aspects of MIC of carbon steel, a material frequently associated with MIC failures and widely used in construction and infrastructure globally. The article begins by introducing the process of MIC, then progresses to explore the complexities of various metallurgical factors relevant to MIC in carbon steel. These factors include chemical composition, grain size, grain boundaries, microstructural phases, inclusions, and welds, highlighting their potential influence on MIC processes. This review systematically presents key discoveries, trends, and the limitations of prior research, offering some novel insights into the impact of metallurgical factors on MIC, particularly for the benefit of those already familiar with other aspects of MIC. The article concludes with recommendations for documenting metallurgical data in MIC research. An appreciation of relevant metallurgical attributes is essential for a critical assessment of a material's vulnerability to MIC to advance research practices and to broaden the collective knowledge in this rapidly evolving area of study.

Functional metagenomic analysis of quorum sensing signaling in a nitrifying community.

Quorum sensing (QS) can function to shape the microbial community interactions, composition, and function. In wastewater treatment systems, acylated homoserine lactone (AHL)-based QS has been correlated with the conversion of floccular biomass into microbial granules, as well as EPS production and the nitrogen removal process. However, the role of QS in such complex communities is still not fully understood, including the QS-proficient taxa and the functional QS genes involved. To address these questions, we performed a metagenomic screen for AHL genes in an activated sludge microbial community from the Ulu Pandan wastewater treatment plant (WWTP) in Singapore followed by functional validation of luxI activity using AHL biosensors and LC-MSMS profiling. We identified 13 luxI and 30 luxR homologs from the activated sludge metagenome. Of those genes, two represented a cognate pair of luxIR genes belonging to a Nitrospira spp. and those genes were demonstrated to be functionally active. The LuxI homolog synthesized AHLs that were consistent with the dominant AHLs in the activated sludge system. Furthermore, the LuxR homolog was shown to bind to and induce expression of the luxI promoter, suggesting this represents an autoinduction feedback system, characteristic of QS circuits. Additionally, a second, active promoter was upstream of a gene encoding a protein with a GGDEF/EAL domain, commonly associated with modulating the intracellular concentration of the secondary messenger, c-di-GMP. Thus, the metagenomic approach used here was demonstrated to effectively identify functional QS genes and suggests that Nitrospira spp. maybe QS is active in the activated sludge community.

Histone H3 lysine 36 methyltransferase mobilizes NER factors to regulate tolerance against alkylation damage in fission yeast.

The Set2 methyltransferase and its target, histone H3 lysine 36 (H3K36), affect chromatin architecture during the transcription and repair of DNA double-stranded breaks. Set2 also confers resistance against the alkylating agent, methyl methanesulfonate (MMS), through an unknown mechanism. Here, we show that Schizosaccharomyces pombe (S. pombe) exhibit MMS hypersensitivity when expressing a set2 mutant lacking the catalytic histone methyltransferase domain or a H3K36R mutant (reminiscent of a set2-null mutant). Set2 acts synergistically with base excision repair factors but epistatically with nucleotide excision repair (NER) factors, and determines the timely nuclear accumulation of the NER initiator, Rhp23, in response to MMS. Set2 facilitates Rhp23 recruitment to chromatin at the brc1 locus, presumably to repair alkylating damage and regulate the expression of brc1+ in response to MMS. Set2 also show epistasis with DNA damage checkpoint proteins; regulates the activation of Chk1, a DNA damage response effector kinase; and acts in a similar functional group as proteins involved in homologous recombination. Consistently, Set2 and H3K36 ensure the dynamicity of Rhp54 in DNA repair foci formation after MMS treatment. Overall, our results indicate a novel role for Set2/H3K36me in coordinating the recruitment of DNA repair machineries to timely manage alkylating damage.

A programmable lipid-polymer hybrid nanoparticle system for localized, sustained antibiotic delivery to Gram-positive and Gram-negative bacterial biofilms.

Bacteria enmeshed in an extracellular matrix, biofilms, exhibit enhanced antibiotic tolerance. Coupled with the rapid emergence of multidrug-resistant strains, the current cohorts of antibiotics are becoming ineffective. Alternative antimicrobial approaches are therefore urgently needed to overcome recalcitrant biofilm infections. Here, we propose the use of a non-toxic lipid-polymer hybrid nanoparticle (LPN) system composed of a solid polymer core (i.e. PLGA; poly lactic-co-glycolic acid) and a cationic lipid shell (i.e. DOTAP) for localized, sustained release of antimicrobial agents to bacterial biofilms. LPNs were synthesized through a simple, robust self-assembly approach. LPNs of uniform particle size (i.e. 100-130 nm), efficiently encapsulated (up to 95%) bioimaging molecules or antibiotics and provided controlled release of the latter. The cationic lipid coating enabled the LPN to anchor onto surfaces of a diverse range of Gram-positive and Gram-negative bacterial pathogens, either in the planktonic or biofilm form. Consistently, the LPN formulations reduced more than 95% of biofilm activity at concentrations that were 8 to 32-fold lower than free antibiotics. These data clearly indicate that these novel formulations could be a useful strategy to enhance the efficacy of antimicrobials against planktonic cells and biofilms of diverse species.